The design and optimization of modern engineering thermal systems—such as heat exchangers, electronic cooling devices, renewable energy systems, and geothermal applications—require a deep understanding of complex coupled physical phenomena. These include fluid flow, heat transfer, magnetic field interactions, porous media effects, and geometric complexity. While recent research has increasingly focused on data-driven and artificial intelligence approaches, there remains a critical and ongoing need for robust, high-fidelity numerical methods to solve the underlying fundamental physics described by coupled nonlinear partial differential equations.This Special Issue aims to bring together original research articles and comprehensive review papers on the development and application of advanced numerical methods for thermo-fluid dynamics in complex engineering systems. Topics of interest include, but are not limited to, natural and mixed convection, nanofluid and hybrid nanofluid flows, magnetohydrodynamic (MHD) effects, flows in porous media (using models such as Darcy, Brinkman, and Forchheimer), heat transfer enhancement strategies, entropy generation analysis, and thermodynamic optimization. The issue seeks to bridge the gap between theoretical numerical developments and their practical application in engineering design, offering a platform for researchers to share cutting-edge computational techniques and their applications.